From 53d471aa22aa18c704ce2ee1c2085ba65cb8bb1b Mon Sep 17 00:00:00 2001
From: Alexander Boettcher <alexander.boettcher@genode-labs.com>
Date: Tue, 30 Sep 2014 15:40:16 +0200
Subject: [PATCH] nova: handle race during signal setup phase

Fixes #1266
---
 .../signal_session/source_rpc_object.h        | 55 ++++++++++++++-----
 .../src/core/signal_source_component.cc       |  3 +-
 2 files changed, 43 insertions(+), 15 deletions(-)

diff --git a/repos/base-nova/include/signal_session/source_rpc_object.h b/repos/base-nova/include/signal_session/source_rpc_object.h
index 8ed857f5f1..4a05cf5f42 100644
--- a/repos/base-nova/include/signal_session/source_rpc_object.h
+++ b/repos/base-nova/include/signal_session/source_rpc_object.h
@@ -22,23 +22,52 @@
 #include <base/rpc_server.h>
 #include <signal_session/nova_source.h>
 
-namespace Genode {
+namespace Genode { struct Signal_source_rpc_object; }
 
-	struct Signal_source_rpc_object : Rpc_object<Nova_signal_source, Signal_source_rpc_object>
-	{
-		protected:
+struct Genode::Signal_source_rpc_object : Rpc_object<Nova_signal_source,
+                                                     Signal_source_rpc_object>
+{
+	private:
 
-			Native_capability _blocking_semaphore;
+		Native_capability _blocking_semaphore;
+		bool              _missed_wakeup;
 
-		public:
+	protected:
 
-			void _register_semaphore(Native_capability const &cap)
-			{
-				if (_blocking_semaphore.valid())
-					PWRN("overwritting blocking signal semaphore !!!");
-				_blocking_semaphore = cap;
+		void _wakeup_client()
+		{
+			if (!_blocking_semaphore.valid()) {
+				_missed_wakeup = true;
+				return;
 			}
-	};
-}
+
+			if (_missed_wakeup)
+				_missed_wakeup = false;
+
+			/* wake up client */
+			uint8_t res = Nova::sm_ctrl(_blocking_semaphore.local_name(),
+			                            Nova::SEMAPHORE_UP);
+			if (res != Nova::NOVA_OK) {
+				PWRN("%s - signal delivery failed - error %x",
+				     __func__, res);
+				_missed_wakeup = true;
+			}
+		}
+
+	public:
+
+		void _register_semaphore(Native_capability const &cap)
+		{
+			if (_blocking_semaphore.valid())
+				PWRN("overwritting blocking signal semaphore !!!");
+
+			_blocking_semaphore = cap;
+
+			if (_missed_wakeup)
+				_wakeup_client();
+		}
+
+		Signal_source_rpc_object() : _missed_wakeup(false) {}
+};
 
 #endif /* _INCLUDE__SIGNAL_SESSION__SOURCE_SERVER_H_ */
diff --git a/repos/base-nova/src/core/signal_source_component.cc b/repos/base-nova/src/core/signal_source_component.cc
index cb412a53f9..9a502f536e 100644
--- a/repos/base-nova/src/core/signal_source_component.cc
+++ b/repos/base-nova/src/core/signal_source_component.cc
@@ -46,8 +46,7 @@ void Signal_source_component::submit(Signal_context_component *context,
 	if (!context->is_enqueued()) {
 		_signal_queue.enqueue(context);
 
-		/* wake up client */
-		Nova::sm_ctrl(_blocking_semaphore.local_name(), Nova::SEMAPHORE_UP);
+		_wakeup_client();
 	}
 }